State-of-the-art implantable Ni/Cd rechargeable batteries used in ventricular assist systems (VAS) offer barely adequate energy density and cycle life. Advances in rechargeable battery technology would greatly improve the day-to-day comfort of patients while simultaneously reducing the need for surgery to replace worn out cells. While rechargeable lithium batteries excel with respect to energy density, the best currently available Li systems only afford 50% of the cycle-life of modern Ni-Cad batteries. In Phase I we will investigate a new strategy for dramatically increasing the cycle-life of Li batteries based on a new class of high performance solvents. These solvents will be evaluated against Li for chemical and electrochemical stability. Finally, electrolytes comprising these new solvents and a salt will be cycled in full Li/TiS2 test vehicles. These advanced Li batteries are expected to afford from three to five times the cycle life of current rechargeable Li systems.